Battery-tobattery charger with push-pull converter.. need design

[l3770ct]

Hi guys..
I'm doing final project for college..
I'm going to make a battery charger that has a source from battery, so it's battery to battery charger
I've planned to used push-pull topology..
is there anybody who have done this and can you explain to me where i should start?
thanks

 

[wally7856]

What voltage battery are you charging from and what voltage battery are you trying to charge. And what kind of battery's.

 

[l3770ct]

What voltage battery are you charging from and what voltage battery are you trying to charge. And what kind of battery's.

source side : 24 VDC 60 Ah, lead acid
load side : 72 VDC 60 Ah, calcium mf
and also i'll use PI controller to control the pwm
can you help me and give me some details please?
thanks

 

[wally7856]

You will have to use a “boost” converter to get the voltage up to 72vdc, plus a few volts more to push some current.

http://en.wikipedia.org/wiki/Boost_converter

You have to know the charging characteristics of your target battery so you know how to taper off the charging.

You will need a monitor circuit for your source battery to stop charging when the source battery is to low, or you will ruin it.

Your PI circuit will need to be powered by a low voltage source that you will have to provide from the battery, either an “buck” converter or an inefficient linear converter.

http://en.wikipedia.org/wiki/Buck_converter

5 volts would be the best starting point. Hopefully you can find some logic level fet’s for the pwm so you only need one low voltage supply.

You will have to decide if you want reverse polarity detection. If the input battery is reversed the charger will not run. If the charging battery is reversed your circuit may blow up or the battery will be ruined.

All of the converters you need can be simple non isolated one transistor circuits. This would be a plus for you because you can have a common ground through the whole system. Realistic power levels for a boost converter are around 150 watts. So you could get 2 amps charging current. If you want much more then that then you will have to use the push pull you mentioned or a forward converter, however this would probably quad-drupal the complexity.

 

[l3770ct]

You will have to use a “boost” converter to get the voltage up to 72vdc, plus a few volts more to push some current.

http://en.wikipedia.org/wiki/Boost_converter

You have to know the charging characteristics of your target battery so you know how to taper off the charging.

You will need a monitor circuit for your source battery to stop charging when the source battery is to low, or you will ruin it.

Your PI circuit will need to be powered by a low voltage source that you will have to provide from the battery, either an “buck” converter or an inefficient linear converter.

http://en.wikipedia.org/wiki/Buck_converter

5 volts would be the best starting point. Hopefully you can find some logic level fet’s for the pwm so you only need one low voltage supply.

You will have to decide if you want reverse polarity detection. If the input battery is reversed the charger will not run. If the charging battery is reversed your circuit may blow up or the battery will be ruined.

All of the converters you need can be simple non isolated one transistor circuits. This would be a plus for you because you can have a common ground through the whole system. Realistic power levels for a boost converter are around 150 watts. So you could get 2 amps charging current. If you want much more then that then you will have to use the push pull you mentioned or a forward converter, however this would probably quad-drupal the complexity.

Why I can't use push-pull converter?
what if I use step-up transformer for the push-pull converter so I can level up the voltage?

and can you explain a lil bit more about how to design monitor circuit and polarity detector you described above and what should I use for both of them?
thanks

 

[wally7856]

“Why I can't use push-pull converter?”

You can use a push pull converter.

“If you want much more then that then you will have to use the push pull you mentioned or a forward converter, however this would probably quad-drupal the complexity."

“and can you explain a lil bit more about how to design monitor circuit and polarity detector you described above and what should I use for both of them?"

The voltage monitor circuit would be an op amp comparator circuit with hysteresis.

http://www.ecircuitcenter.com/circuits/op_comp/op_comp.htm

A polarity detector can be as simple as an opto coupler connected to the battery terminals. The pwm circuit would be held off until the opto coupler gave a signal that the battery was connected properly.

 

[l3770ct]

“Why I can't use push-pull converter?”

You can use a push pull converter.

“If you want much more then that then you will have to use the push pull you mentioned or a forward converter, however this would probably quad-drupal the complexity."

“and can you explain a lil bit more about how to design monitor circuit and polarity detector you described above and what should I use for both of them?"

The voltage monitor circuit would be an op amp comparator circuit with hysteresis.

http://www.ecircuitcenter.com/circuits/op_comp/op_comp.htm

A polarity detector can be as simple as an opto coupler connected to the battery terminals. The pwm circuit would be held off until the opto coupler gave a signal that the battery was connected properly.

then, what charging method should I use to get the best performance?

correction : I use calcium mf battery on both source and load side

in addition, i use it for electric vehicle..
source battery will be in charging station and the load battery will be in the car itself